Certain electrical circuits, in particular those circuits that amplify or otherwise process electrical signals, are sensitive to electromagnetic interference. This interference can originate from many sources, and is common in the everyday operating environment of consumer and industrial electronics. Interfering signals can cause numerous problems, ranging from relatively minor inconveniences (such as distortion in an audio signal), to significant problems such as malfunction of a computer or other deivce. In order to eliminate this interference, a conductive metal cover is typically placed around the sensitive circuitry to shield the circuitry by conducting the interference to ground. In this way, the metal cover effectively filters out all unwanted signals and provides an electrically "clean" environment around the circuit.
Conventional shielding methods consist of placing the circuit into a metal "can" (enclosure) and attaching a cover to provide complete electromagnetic isolation. Regrettably, the attachment of this can and cover increases material costs, increases labor costs, increases the complexity of the finished product, and reduces overall mechanical reliability.
Generally a separate shield system requires at least one, and usually two additional parts. These parts are typically custom designed and fabricated, requiring the added expense of designing the parts, designing the tooling necessary to fabricate the parts, and manufacturing the parts. These costs are not trival, and typically run as much as 10-100% of the cost of the circuit being shielded. In certain situations, provision must be made to electrically isolate the interior of the metal enclosure from other areas of the circuit in order to prevent shorting or otherwise damaging the circuit. To do this, an insulating material must be placed between the shield and the circuit, which requires additional material and increases design and assembly costs.
The assembly of these additional parts used in conventional shielding practice requires significant time and space on the factory floor, and as such, further increases the cost of the finished circuit. Because nearly all of the prior shielding mechanisms are unique shapes and sizes, assembly is normally performed manually, leading to higher costs and lower quality than if performed by machines in an automated manufacturing environment.
In certain cases, the circuitry must be rigidly mounted in the metal shield to prevent unwanted distortion of the signal from mechanical microphonics. Such rigid mounting gives rise to unwanted mechanical stresses when the finished unit is exposed to thermal excursions, since the circuit material and the shielding material are made from two distinct materials, having unique and differing coefficients of thermal expansion. These stresses can result in mechanical distortion of the circuit or shield, or even to catastrophic failure of the circuit due to a discontinuous electrical connection between the circuit and the shield.